Abstract: Traditional DC traction power supply systems of urban rail transit generally adopt 24-pulse rectifier units, which only support unidirectional power transmission and fail to recover the regenerative braking energy of trains, resulting in prominent energy loss. Taking Suzhou Metro Line 3 as the research object, this paper establishes the equivalent circuit and simulation model of the traction power supply system, and compares the structure, principle and electrical characteristics between conventional rectifier units and bidirectional converters. Simulation tests are carried out on the external characteristics of converters and train departure intervals. The results show that bidirectional converters realize bidirectional power flow and efficiently recycle regenerative energy with remarkable energy-saving performance. Proper matching of equipment characteristics and train operation schedules can further reduce the total line energy consumption. The conclusions can provide references for energy-saving renovation, equipment selection and operation strategy optimization of metro power supply systems.